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New here (and spur gear constraint)

Discussion in 'Using Alibre Design' started by singultus, Oct 10, 2018.

  1. singultus

    singultus New Member

    Hey guys!
    I'm new here and just messing around with my new Atom3d. I worked through the "Alibre Atom3d Exercise Manual" which gave a rather good introduction for somebody who never used a CAD software before. Right now a found a spur gear template in the depth of this forum. Atom3d seems to lack the "configuration" why the gears can't be modified. I will attempt to design one on my own, however, I was wondering whether there will be proper constraints in assembly to actually simulate the gears meshing. I still habe some troubles folding my mind about the whole quick constrain thing.
    Cheers singultus
  2. JST

    JST Alibre Super User

    No, there are NO constraints that even simulate the meshing of gears, let alone allow actual meshing. There is a workaround that has allowed linking two shafts, but it has problems in my experience

    Yes, they are needed, at least a "settable ratio" relation between shafts etc, for pulley and gear type operation.

    No, I am not asking for a "full animation for free", that has many more considerations and capabilities than simply having some more available constraints. I am perfectly happy with a "manual animation" that at leasy allows verification of operation, even if there is some hassle involved with doing it.

    I have NEVER USED the "quick constraints". I always use the full constraint menu, I find that to be easier in the long run. The other does have an "undo", but seemingly does not include all the constraints possible, and I just do not wish to have to decide "if I can do it with the quick", or "if I need the full". Simpler to always use the full and have no questions..

    The "undo" needs to be in the main constraint menu as well.
  3. singultus

    singultus New Member

    Hmm, ok. Could you elaborate on the workaround? Moreover, Atom3d seems to lack the full constraints menu... Or am I to dumb to find it?
  4. JST

    JST Alibre Super User

    No clue on Atom.

    The workaround involved setting up a feature on each shaft, and then linking them via the "angle" constraint, as I recall. It worked for a turn or so, but would fail.

    Been a couple years since I tried it, there was a thread on it, that you may be able to get "search" to find. I was not successful finding it, likely wrong search terms.
  5. Max

    Max Administrator Staff Member

    The Quick Constrain mode lacks the Orient Constraint, but has all the others. However, the Orient Constraint is basically an Angle Constraint of Angle = 0. So, you aren't really missing anything, since you can just make an angle constraint with Angle = 0. Moreover, if you Edit a constraint (Right Click a constraint > Edit) you are presented the "full" constraint menu. It just isn't an option in the toolbar, so if you're desperate for an Orient constraint for some reason, just create any constraint then edit it to be an Orient constraint.

    Here is an example of this gear scenario:

    Step 1: Open the Package file (download below)
    Step 2: Right click on each gear > Show Reference Geometry
    Step 3: Hover over each Angle constraint. Notice that we picked a neutral plane in the assembly and made an angle constraint against that plane and one of the neutral planes in each part (the part's reference geometry)
    Step 4: Right Click > Edit the "Large Gear Angle" constraint. Notice it takes the form:
    • A1*(2/5)+3.6°
      • The A1 * (2/5) part defines the gear ratio. The small gear has 20 teeth, the large gear has 50. A1 is the Parameter name for the Angle definition for the other gear. You can see all available parameters, and rename them, by clicking this button, located in almost every dialog:
      • The +3.6 component offsets the angle by a set amount, so you make them mesh together. This is something you eyeball.
    Step 5: Right Click > Edit the "Small Gear Angle" constraint. This is the A1 parameter. Turn on Preview and press the up or down arrow on the input box:

    As you do this, what is happening is the angle of the small gear is generating a number (12 in the example box shown above). The angle for the second gear is being evaluated with the equation 12 degrees * (2/5) + 3.6, and is updating. The appearance is that the gears now mesh together and turn at the correct ratio.

    It's not a perfect solution, but it'll get you a certain amount of far.


    Attached Files:

    Last edited: Oct 11, 2018
  6. singultus

    singultus New Member

    Thanks for the very detailed answer! This is great, assuming I'll be able to connect several gears in this way.
    Given properly meshing gears the offset angle can also be calculated instead of eyeballed: 360°/tooth_count/2
    Cheers singultus

    PS: I had a look at your gear part. How did you produce the base sketch of the involute gear? Is the 2d part somehow imported?
  7. Max

    Max Administrator Staff Member

    I used Alibre Script which is available in Pro and Expert. It will at some point be available in Atom3D, probably with our 2019 release, so if you're on the Update Plan you can get that.
  8. albie0803

    albie0803 Alibre Super User

    Don't forget that unless you are creating models to 3d print or machine from, true tooth form is not really important, its just a visual cue.
    If you are interested I can give you a model that you adjust parameters in which will give you a reasonably good tooth for visual purposes.
    You enter the OD, Root Diameter, face width, number of teeth and bore size and it recalculates. You can even do helical gears by entering an angle. I use this for all my drawings.
  9. MilesH

    MilesH Alibre Super User

    If you want a 'motor' function you can use the Precise Placement tool. Set axis to centre of motor shaft, enter a low degree rotation value and hold down the Enter key.
  10. singultus

    singultus New Member

    Thanks for all the inputs!
    @albie0803: Having a look at your template would be great. Please keep in mind, that "configurations" are not included in atom. I found such a template in the forums, could open it but couldn't edit it due to this limitation. I tried to build something similar on my own (using https://www.fictiv.com/blog/posts/creating-involute-gears-in-cad), however I'm still struggling a little bit.
  11. albie0803

    albie0803 Alibre Super User

    Here is the gear template. It doesn't use Configurations. Open the Equation Editor f(x) under Parameters and adjust the top 9 parameters that start with a_
    The last one a_toothvar will change the shape of the tooth, making the top thinner or thicker.
    As you select each variable, look at the bottom for comments that explain things.
    Set the helix to 0 for a spur gear.

    As I said previously, this will give you a good basic shape for teeth on a gear only. These are not true involute tooth forms, so trying to 3d print them wont work. They work for us because we have proper gear hobbers and all that needs to be accurate is the OD for the turners, the rest just happens.

    If you really need true involute spur gears I can provide you with correct DXFs from gear software we have.

    Attached Files:

  12. EngineerJim

    EngineerJim New Member

    It's great to see that there is a constraint capability to run round gears. However, I have a drawing where I need to constrain two linear gears to a round one (like how an expandable dining room table works). Is there a way to do this in Alibre? If not, I was wondering if there's a constraint method to make two objects maintain an equal distance from a reference plane but mirrored so one part is on one side of the plane and the other part is on the other side of the plane. Then as you move one closer to the plane the other moves closer to the plane as well (by the same amount).
  13. DavidJ

    DavidJ Alibre Super User

    An assembly mirror will work in real time. Most other tricks only update the display when you release the dragged part. Assembly mirror also seems to work regardless of which part you drag. Might be worth experimenting with.
  14. idslk

    idslk Senior Member

  15. HaroldL

    HaroldL Alibre Super User

    Isn't that called a rack and pinion? In your example it may even be called a dual rack and pinion.

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